the ocean is HUGE, and the things are designed to allow current to flow though them.
Think of it this way. Do windmills change air currents and effect the weather?
The effect it would have on the oceanic current is so minor, that you wouldn't even be able to measure it.
the only other question could be, does it effect wild life?

Question: With enough of these, would the resistance disrupt the flow of the currents enough to affect the climate/ecosystem on earth?